Composite absorbent particles

ABSTRACT

Composite particles and methods for making the same. An absorbent material is formed into a particle. An optional performance-enhancing active is coupled to the absorbent material before, during, or after the particle-forming process, homogeneously and/or in layers. Additionally, the composite absorbent particle may include a core material. Preferred methods for creating the absorbent particles include a pan agglomeration process, a high shear agglomeration process, a low shear agglomeration process, a high pressure agglomeration process, a low pressure agglomeration process, a rotary drum agglomeration process, a mix muller process, a roll press compaction process, a pin mixer process, a batch tumble blending mixer process, an extrusion process, and a fluid bed process.

RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 15/281,620, filedSep. 30, 2016, which is a continuation of U.S. Ser. No.: 14/985,180,filed Dec. 30, 2015, which is a continuation of U.S. Ser. No.:13/758,030, filed Feb. 4, 2013, now U.S. Pat. No. 9,253,961, which is acontinuation of U.S. Ser. No.: 12/032,450, filed Feb. 15, 2009, nowabandoned, which is a continuation of U.S. Ser. No. 10/861,044, filedJun. 4, 2004, now abandoned, which is a continuation-in-part of U.S.Ser. No. 10/618,401, filed Jul. 11, 2003, now abandoned. U.S. Ser. No.10/861,044 is also a continuation-in-part of U.S. Ser. No.: 10/773,585,filed Feb. 6, 2004, now abandoned, all of which are herein incorporatedby reference.

FIELD OF THE INVENTION

The present invention relates to composite absorbent particles, and moreparticularly, this invention relates to a composite absorbent particlehaving improved clumping and odor-inhibiting properties.

BACKGROUND OF THE INVENTION

Clay has long been used as a liquid absorbent, and has found particularusefulness as an animal litter.

Because of the growing number of domestic animals used as house pets,there is a need for litters so that animals may micturate, void orotherwise eliminate liquid or solid waste indoors in a controlledlocation. Many cat litters use clay as an absorbent. Typically, the clayis mined, dried, and crushed to the desired particle size.

Some clay litters have the ability to clump upon wetting. For example,sodium bentonite is a water-swellable clay which, upon contact withmoist animal waste, is able to agglomerate with other moistened sodiumbentonite clay particles. The moist animal waste is contained by theagglomeration of the moist clay particles into an isolatable clump,which can be removed from the container (e.g., litterbox) housing thelitter. However, the clump strength of clay litters described above istypically not strong enough to hold the clump shape upon scooping, andinevitably, pieces of the litter break off of the clump and remain inthe litter box, allowing waste therein to create malodors. Further, rawclay typically has a high clump aspect ratio when urinated in. Theresult is that the wetted portion of clay will often extend to thecontainer containing it and stick to the side or bottom of thecontainer.

What is needed is an absorbent material suitable for use as a catlitter/liquid absorbent that has better clumping characteristics, i.e.,clump strength and aspect ratio, than absorbent materials heretoforeknown.

Another problem inherent in typical litters is the inability toeffectively control malodors. Clay has very poor odor-controllingqualities, and inevitably waste build-up leads to severe malodorproduction. One attempted solution to the malodor problem has been theintroduction of granular activated carbon (GAC) into the litter.However, the GAC is usually dry blended with the litter, making thelitter undesirably dusty. Also, the GAC concentration must typically be1% by weight or higher to be effective. Activated carbon is veryexpensive, and the need for such high concentrations greatly increasesproduction costs. Further, because the clay and GAC particles are merelymixed, the litter will have GAC concentrated in some areas, andparticles with no GAC in other areas.

The human objection to odor is not the only reason that it is desirableto reduce odors. Studies have shown that cats are territorial animalsand will often “mark” litter that has little or no smell with theirpersonal odor, such as by urinating. When cats return to the litterboxand don't sense their odor, they will try to mark their territory again.The net effect is that cats will return to use a litter box more oftenif the odor of their markings are reduced. Thus, a litter that iseffective at eliminating or hiding a cat's personal odor can encouragethe animal to use a litter box rather than depositing waste outside thebox.

What is needed is an absorbent material with improved odor-controllingproperties, and that maintains such properties for longer periods oftime.

What is further needed is an absorbent material with improvedodor-control, yet requiring much lower concentrations of odorcontrolling actives.

What is still further needed is an absorbent material with a lower bulkdensity while maintaining a high absorbency rate comparable to orexceeding heretofore known materials.

What is also needed is an absorbent material suitable for an animallitter which encourages animals to micturate and void on the absorbentmaterial.

SUMMARY OF THE INVENTION

The present invention provides composite absorbent particles and methodsfor making the same. An absorbent material is formed into a particle,preferably, by an agglomeration process. An optionalperformance-enhancing active is coupled to the absorbent material duringthe agglomeration process, homogeneously and/or in layers. Exemplaryactives include antimicrobials, odor absorbers/inhibitors, binders(liquid/solid, silicate, ligninsulfonate, etc.), fragrances, healthindicating materials, nonstick release agents, and mixtures thereof.Additionally, the composite absorbent particle may include a corematerial.

Methods disclosed for creating the absorbent particles include a panagglomeration process, a high shear agglomeration process, a low shearagglomeration process, a high pressure agglomeration process, a lowpressure agglomeration process, a rotary drum agglomeration process, amix muller process, a roll press compaction process, a pin mixerprocess, a batch tumble blending mixer process, and an extrusionprocess. Fluid bed process may also represent a technique for formingthe inventive particles.

The processing technology disclosed herein allows the “engineering” ofthe individual composite particles so that the characteristics of thefinal product can be predetermined. The composite particles areparticularly useful as an animal litter. Favorable characteristics for alitter product such as odor control, active optimization, low density,low tracking, low dust, strong clumping, etc. can be optimized to givethe specific performance required. Another aspect of the invention isthe use of encapsulated actives, i.e., formed into the particle itselfand accessible via pores or discontinuities in the particles.Encapsulation of actives provides a slow release mechanism such that theactives are in a useful form for a longer period of time. A furtheraspect of the invention provides control over granule strength, andtherefore, degradation and/or disintegration properties. Controlling therate at which granules degrade, for example when the granulesdisintegrate due to urine deposition, provides another mechanism toslowly release actives from the granule's interior and surface, and inso doing, optimize performance. Thus, the present invention's engineeredcomposite particle optimizing the performance enhancing actives is novelin light of the prior art.

Other aspects and advantages of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of the presentinvention, as well as the preferred mode of use, reference should bemade to the following detailed description read in conjunction with theaccompanying drawings.

FIG. 1 illustrates several configurations of absorbent compositeparticles according to various embodiments of the present invention.

FIG. 2 is a process diagram illustrating a pan agglomeration processaccording to a preferred embodiment.

FIG. 3 depicts the structure of an illustrative agglomerated compositeparticle formed by the process of FIG. 2.

FIG. 4 is a process diagram illustrating another exemplary panagglomeration process with a recycle subsystem.

FIG. 5 is a process diagram illustrating an exemplary pin mixer processfor forming composite absorbent particles.

FIG. 6 is a process diagram illustrating an exemplary mix muller processfor forming composite absorbent particles.

FIG. 7 is a graph depicting malodor ratings.

FIG. 8 depicts the clumping action of composite absorbent particlesaccording to a preferred embodiment.

FIG. 9 depicts disintegration of a composite absorbent particleaccording to a preferred embodiment.

BEST MODES FOR CARRYING OUT THE INVENTION

The following description includes the best embodiments presentlycontemplated for carrying out the present invention. This description ismade for the purpose of illustrating the general principles of thepresent invention and is not meant to limit the inventive conceptsclaimed herein.

The present invention relates generally to composite absorbent particleswith improved physical and chemical properties comprising an absorbentmaterial and optional performance-enhancing actives. By using variousprocesses described herein, such particles can be “engineered” topreferentially exhibit specific characteristics including but notlimited to improved odor control, lower density, easier scooping, betterparticle/active consistency, higher clump strength, etc. One of the manybenefits of this technology is that the performance-enhancing activesmay be positioned to optimally react with target molecules such as butnot limited to odor causing volatile substances, resulting in surprisingodor control with very low levels of active ingredient.

A preferred use for the absorbent particles is as a cat litter, andtherefore much of the discussion herein will refer to cat litterapplications. However, it should be kept in mind that the absorbentparticles have a multitude of applications, such as air and waterfiltration, fertilizer, waste remediation, etc., and should not belimited to the context of a cat litter.

One preferred method of forming the absorbent particles is byagglomerating granules of an absorbent material in a pan agglomerator. Apreferred pan agglomeration process is set forth in more detail below,but is described generally here to aid the reader. Generally, thegranules of absorbent material are added to an angled, rotating pan. Afluid or binder is added to the granules in the pan to cause binding ofthe granules. As the pan rotates, the granules combine or agglomerate toform particles. Depending on pan angle and pan speed among otherfactors, the particles tumble out of the agglomerator when they reach acertain size. The particles are then dried and collected.

One or more performance-enhancing actives are preferably added to theparticles in an amount effective to perform the desired functionality orprovide the desired benefit. For example, these actives can be addedduring the agglomeration process so that the actives are incorporatedinto the particle itself, or can be added during a later processingstep.

FIG. 1 shows several embodiments of the absorbent particles of thepresent invention. These particles have actives incorporated:

-   -   1. In a layer on the surface of a particle (102)    -   2. Evenly (homogeneously) throughout a composite litter particle        (104)    -   3. In a concentric layer(s) throughout the particle and/or        around a core (106)    -   4. In pockets or pores in and/or around a particle (108)    -   5. In a particle with single or multiple cores (110)    -   6. Utilizing non-absorbent cores (112)    -   7. No actives (114)    -   8. No actives, but with single or multiple cores (116)    -   9. In any combination of the above

As previously recited hereinabove, other particle-forming processes maybe used to form the inventive particles of the present invention. Forexample, without limitation, extrusion and fluid bed processes appearappropriate. Extrusion process typically involves introducing a solidand a liquid to form a paste or doughy mass, then forcing through a dieplate or other sizing means. Because the forcing of a mass through a diecan adiabatically produce heat, a cooling jacket or other means oftemperature regulation may be necessary. The chemical engineeringliterature has many examples of extrusion techniques, equipment andmaterials, such as “Outline of Particle Technology,” pp. 1-6 (1999),“Know-How in Extrusion of Plastics (Clays) or NonPlastics (CeramicOxides) Raw Materials, pp. 1-2, “Putting Crossflow Filtration to theTest,” Chemical Engineering, pp. 1-5 (2002), and Brodbeck et al., U.S.Pat. No. 5,269,962, especially col. 18, lines 30-61 thereof, all ofwhich is incorporated herein by reference thereto. Fluid bed process isdepicted in Coyne et al., U.S. Pat. No. 5,093,021, especially col. 8,line 65 to col. 9, line 40, incorporated herein by reference.

Materials

Many liquid-absorbing materials may be used without departing from thespirit and scope of the present invention. Illustrative absorbentmaterials include but are not limited to minerals, fly ash, absorbingpelletized materials, perlite, silicas, other absorbent materials andmixtures thereof. Preferred minerals include: bentonites, zeolites,fullers earth, attapulgite, montmorillonite diatomaceous earth, opalinesilica, crystalline silica, silica gel, alumina, Georgia White clay,sepiolite, calcite, dolomite, slate, pumice, tobermite, marls,attapulgite, kaolinite, halloysite, smectite, vermiculite, hectorite,Fuller's earth, fossilized plant materials, expanded perlites, gypsumand other similar minerals and mixtures thereof. The preferred absorbentmaterial is sodium bentonite having a mean particle diameter of about5000 microns or less, preferably about 3000 microns or less, and ideallyin the range of about 25 to about 150 microns.

Because minerals, and particularly clay, are heavy, it is may bedesirable to reduce the weight of the composite absorbent particles toreduce shipping costs, reduce the amount of material needed to need tofill the same relative volume of the litter box, and to make thematerial easier for customers to carry. To lower the weight of eachparticle, a lightweight core material, or “core,” may be incorporatedinto each particle. The core can be positioned towards the center of theparticle with a layer or layers of absorbent and/or active surroundingthe core in the form of a shell. This configuration increases the activeconcentration towards the outside of the particles, making the activemore effective. The shell can be of any desirable thickness. In oneembodiment with a thin shell, the shell has an average thickness of lessthan about ½ that of the average diameter of the particle, andpreferably the shell has an average thickness of not less than about1/16 that of the average diameter of the particle. More preferably, theshell has an average thickness of between about 7/16 and ⅛ that of theaverage diameter of the particle, even more preferably less than about ½that of the average diameter of the particle, and ideally between about⅜ and ⅛ that of the average diameter of the particle. Note that theseranges are preferred but not limiting.

According to another embodiment comprising a core and absorbent materialsurrounding the core in the form of a shell, an average thickness of theshell is at least about four times an average diameter of the core. Inanother embodiment, an average thickness of the shell is between about 1and about 4 times an average diameter of the core. In yet anotherembodiment, an average thickness of the shell is less than an averagediameter of the core. In a further embodiment, an average thickness ofthe shell is less than about one-half an average diameter of the core.

Other ranges can be used, but the thickness of the shell of absorbentmaterial/active surrounding a non-clumping core should be balanced toensure that good clumping properties are maintained.

In another embodiment, the absorbent material “surrounds” a core (e.g.,powder, granules, clumps, etc.) that is dispersed homogeneouslythroughout the particle or in concentric layers. For example, alightweight or heavyweight core material can be agglomeratedhomogeneously into the particle in the same way as the active. The corecan be solid, hollow, absorbent, nonabsorbent, and combinations ofthese.

Exemplary lightweight core materials include but are not limited tocalcium bentonite clay, Attapulgite clay, Perlite, Silica, non-absorbentsilicious materials, sand, plant seeds, glass, polymeric materials, andmixtures thereof. A preferred material is a calcium bentonite-containingclay which can weigh about half as much as bentonite clay. Calciumbentonite clay is non-clumping so it doesn't stick together in thepresence of water, but rather acts as a seed or core. Granules ofabsorbent material and active stick to these seed particles during theagglomeration process, forming a shell around the seed.

Using the above lightweight materials, a bulk density reduction of ≧10%,≧20%, preferably ≧30%, more preferably ≧40%, and ideally ≧50% can beachieved relative to generally solid particles of the absorbent material(e.g., as mined) and/or particles without the core material(s). Forexample, in a particle in which sodium bentonite is the absorbentmaterial, using about 50% of lightweight core of calcium bentonite clayresults in about a 42% bulk density reduction.

Heavyweight cores may be used when it is desirable to have heavierparticles. Heavy particles may be useful, for example, when theparticles are used in an outdoor application in which high winds couldblow the particles away from the target zone. Heavier particles alsoproduce an animal litter that is less likely to be tracked out of alitter box. Illustrative heavyweight core materials include but are notlimited to sand, iron filings, etc.

Note that the bulk density of the particles can also be adjusted(without use of core material) by manipulating the agglomeration processto increase or decrease pore size, pore volume and surface area of theparticle.

Note that active may be added to the core material if desired. Further,the core can be selected to make the litter flushable. One such corematerial is wood pulp.

Illustrative materials for the performance-enhancing active(s) includebut are not limited to antimicrobials, odor absorbers/inhibitors,binders, fragrances, health indicating materials, nonstick releaseagents, superabsorbent materials, and mixtures thereof. One greatadvantage of the particles of the present invention is thatsubstantially every absorbent particle contains active.

Preferred antimicrobial actives are boron containing compounds such asborax pentahydrate, borax decahydrate, boric acid, polyborate,tetraboric acid, sodium metaborate, anhydrous, boron components ofpolymers, and mixtures thereof.

One type of odor absorbing/inhibiting active inhibits the formation ofodors. An illustrative material is a water soluble metal salt such assilver, copper, zinc, iron, and aluminum salts and mixtures thereof.Preferred metallic salts are zinc chloride, zinc gluconate, zinclactate, zinc maleate, zinc salicylate, zinc sulfate, zinc ricinoleate,copper chloride, copper gluconate, and mixtures thereof. Other odorcontrol actives include nanoparticles that may be composed of manydifferent materials such as carbon, metals, metal halides or oxides, orother materials. Additional types of odor absorbing/inhibiting activesinclude cyclodextrin, zeolites, silicas, activated carbon (also known asactivated charcoal), acidic, salt-forming materials, and mixturesthereof. Activated alumina (Al₂O₃) has been found to provide odorcontrol comparable and even superior to other odor control additivessuch as activated carbon, zeolites, and silica gel. Alumina is a whitegranular material, and is properly called aluminum oxide.

The preferred odor absorbing/inhibiting active is Powdered ActivatedCarbon (PAC), though Granular Activated Carbon (GAC) can also be used.PAC gives much greater surface area than GAC (GAC is something largerthan powder (e.g., ≧80 mesh U.S. Standard Sieve (U.S.S.S.))), and thushas more sites with which to trap odor-causing materials and istherefore more effective. PAC has only rarely been used in absorbentparticles, and particularly animal litter, as it tends to segregate outof the litter during shipping, thereby creating excessive dust (alsoknown as “sifting”). By agglomerating PAC into particles, the presentinvention overcomes the problems with carbon settling out duringshipping. Generally, the preferred mean particle diameter of the carbonparticles used is less than about 500 microns, but can be larger. Theparticle size can also be much smaller (less than 100 nanometers) as inthe case of carbon nanoparticles. The preferred particle size of the PACis about 150 microns (˜100 mesh U.S.S.S.) or less, and ideally in therange of about 25 to 150 microns, with a mean diameter of about 50microns (˜325 mesh U.S.S.S.) or less.

An active may be added to reduce or even prevent sticking of the litterto the litter box. Useful anti-stick agents include, but are not limitedto, hydrophobic materials such as activated carbon, carbon black,Teflon®, hydrophobic polymers and co-polymers, for examplepoly(propylene oxide).

How tightly swelled litter sticks to a litter box can be measured as afunction of the force necessary to remove the ‘clump’. One method ofmeasuring this force uses 150 cc of litter and 20 cc of pooled cat urine(from several cats so it is not specific) to form a clump on the bottomof a cat box. The urine causes the litter to clump, and in so doing, theswelled litter adheres to the litter box. The relative amount of force(in pounds) necessary to remove the adhered clump is measured using anInstron tensile tester and a modified scooper.

The data in the table below refer to the following formulas. Formula Pis composed of composite particles of the present invention that contain0.5% PAC as an anti-stick agent. Formula S is a commercially availablegranular clay litter with no added anti-stick agents.

The data in the table below show that a urine clump formed from theformula composed of composite particles containing 0.5% PAC as ananti-stick agent requires less force for removal from the bottom of acat box than a urine clump formed from a commercially available granularclay litter containing no anti-stick agents.

TABLE 1 Formula S Litter height Formula P Removal Force in InchesRemoval Force in pounds pounds 0.5 0.17 0.63 0.25 0.46 0.81

Generally, PAC is effective to reduce sticking when present in thecomposite particles in an amount of 0.1% or more, preferably in therange of about 0.1 to about 1.0%, when compared to composite particlesnot having the PAC present.

The active may also include a binder such as water, lignin sulfonate(solid), polymeric binders, fibrillated Teflon® (polytetrafluoroethyleneor PTFE), and combinations thereof. Useful organic polymerizable bindersinclude, but are not limited to, carboxymethylcellulose (CMC) and itsderivatives and its metal salts, guar gum cellulose, xanthan gum,starch, lignin, polyvinyl alcohol, polyacrylic acid, styrene butadieneresins (SBR), and polystyrene acrylic acid resins. Water stableparticles can also be made with crosslinked polyester network, includingbut not limited to those resulting from the reactions of polyacrylicacid or citric acid with different polyols such as glycerin, polyvinylalcohol, lignin, and hydroxyethylcellulose.

Another active that can be added to the composite particles is a clumpenhancing agent that is activated by contact with a liquid to strengthenclumps, thereby assisting in the isolation and encapsulation of theoffensive material. Clump enhancing agents are particularly useful whenthe composite particles are formed of materials that do not have stronginherent clumping capabilities, and where other non-clumping performanceenhancing actives are formed on an outer surface of the particles.Preferred clump enhancing agents include binders, gums, starches, andadhesive polymers.. The clump enhancing agent is preferably added toouter surfaces of the particles by spraying or by addition during thefinal stages of agglomeration. Clump enhancing agents can also bebulk-added to the composite particles.

Dedusting agents can also be added to the particles in order to reducethe dust level in the final product. All of the clump enhancing agentslisted above are effective dedusting agents when applied to the outersurface of the composite absorbent particles. Other dedusting agentsinclude but are not limited to fibrillated Teflon, resins, water, andother liquid or liquefiable materials.

A color altering agent such as a dye, pigmented polymer, metallic paint,bleach, lightener, etc. may be added to vary the color of absorbentparticles, such as to darken or lighten the color of all or parts of thelitter so it is more appealing. Preferably, the color altering agentcomprises up to approximately 20% of the absorbent composition, morepreferably, 0.001%-5% of the composition. Even more preferably, thecolor altering agent comprises approximately 0.001%-0.1% of thecomposition.

Preferred carriers for the color altering agent are zeolites, carbon,charcoal, etc. These substrates can be dyed, painted, coated withpowdered colorant, etc.

Activated alumina and activated carbon may include an embedded coloringagent that has been added during the fabrication of the activatedalumina or activated carbon particles to form a colored speckle. Theinventors have found that the odor absorbing properties of activatedalumina and activated carbon are not significantly reduced due to theapplication of color altering agents thereto.

Additionally, activated alumina's natural white coloring makes it adesirable choice as a white, painted or dyed “speckle” in litters. Incomposite and other particles, the activated alumina can also be addedin an amount sufficient to lighten or otherwise alter the overall colorof the particle or the overall color of the entire composition.

Compositions may also contain colored speckles for visual appeal. Otherexamples of speckle material are salt crystals or gypsum crystals.

Large particles of carbon, e.g., activated carbon or charcoal, can alsobe used as a dark speckle. Such particles are preferably within aparticle diameter size range of about 0.01 to 10 times the mean diameterof the other particles in the mixture.

Suitable superabsorbent materials include superabsorbent polymers suchas AN905SH, FA920SH, and F04490SH, all from Floerger. Preferably, thesuperabsorbent material can absorb at least 5 times its weight of water,and ideally more than 10 times its weight of water.

The core mentioned above can also be considered an active, for exampleincluding a lightweight material dispersed throughout the particle toreduce the weight of the particle, a core made of pH-altering material,etc. A preferred embodiment is to bind actives directly to the surfaceof composite absorbent particles. The use of extremely low levels ofactives bound only to the surface of absorbent particles leads to thefollowing benefits:

-   -   1. the use of extremely small particle size of the active        material results in a very high surface area of active while        using a very small amount of active,    -   2. with actives present only on the surface of the substrate,        the waste of expensive actives that would be found with        ‘homogeneous’ composite particles [where actives are found        throughout the substrate particles] is eliminated,    -   3. segregation of actives from substrates is eliminated; thus,        the actives remain dispersed and do not end up on the bottom of        the litter container,    -   4. by using very low levels of expensive actives, the cost of        the product is greatly reduced,    -   5. binding of small particle size actives directly to the        substrate surface results in lower dust levels than in bulk        added product.

Surprisingly, low levels of PAC 0.2-0.3% have been found to provideexcellent odor control in cat litter when they are bound to the surfaceof a material such as sodium bentonite clay. For example, binding ofsmall amounts of PAC particles to sodium bentonite substrate particlesusing xanthan gum or fibrillatable PTFE as binder results in littermaterials with superior odor adsorbing performance. In this example, thePAC is highly effective at capturing malodorous volatile organiccompounds as they escape from solid and liquid wastes due to the highsurface area of the PAC, and its preferred location on the surface ofthe sodium bentonite particles.

Another aspect of the invention is the use of Encapsulated Actives,where the actives are positioned inside the particle, homogeneouslyand/or in layers. Because of the porous structure of the particles, evenactives positioned towards the center of the particle are available toprovide their particular functionality. In addition, as previouslymentioned, controlled degradation of the composite particles can resultin controlled release of encapsulated actives. Encapsulation of activesprovides a slow release mechanism such that the actives are in a usefulform for a longer period of time. This is particularly so where theactive is used to reduce malodors, control or kill germs, reducesticking to the box, enhance clump strength, or as an indicator ofhealth.

Pan Agglomeration and Other Particle Creation Processes

The agglomeration process in combination with the unique materials usedallows the manufacturer to control the physical properties of particles,such as bulk density, dust, strength, as well as PSD (particle sizedistribution) without changing the fundamental composition andproperties of absorbent particles.

One benefit of the pan agglomeration process of the present invention istargeted active delivery, i.e., the position of the active can be“targeted” to specific areas in, on, and/or throughout the particles.Another benefit is that because the way the absorbent particles areformed is controllable, additional benefits can be “engineered” into theabsorbent particles, as set forth in more detail below.

FIG. 2 is a process diagram illustrating a pan agglomeration process 200according to a preferred embodiment. In this example, the absorbentgranules are bentonite clay and the active is PAC. Cores of a suitablematerial, here calcium bentonite clay, are also added. The absorbentparticles (e.g., bentonite powder) is mixed with the active (e.g., PAC)to form a dry mixture, which is stored in a hopper 202 from which themixture is fed into the agglomerator 206. Alternatively, the absorbentgranules and active(s) may be fed to the agglomerator individually. Forexample, liquid actives can be added by a sprayer. The cores arepreferably stored in another hopper 204, from which they are fed intothe agglomerator. A feed curtain can be used to feed the variousmaterials to the agglomerator.

In this example, the agglomerator is a pan agglomerator. The panagglomerator rotates at a set or variable speed about an axis that isangled from the vertical. Water and/or binder is sprayed onto thegranules in the agglomerator via sprayers 208 to raise/maintain themoisture content of the particles at a desired level so that they sticktogether. Bentonite acts as its own binder when wetted, causing it toclump, and so additional binder is not be necessary. The panagglomeration process gently forms composite particles through asnowballing effect broadly classified by experts as natural or tumblegrowth agglomeration. FIG. 3 depicts the structure of an illustrativeagglomerated composite particle 300 formed during the process of FIG. 2.As shown, the particle includes granules of absorbent material 302 andactive 304 with moisture 306 or binder positioned interstitially betweenthe granules.

Depending on the pan angle and pan speed, the particles tumble off uponreaching a certain size. Thus, the pan angle and speed controls how bigthe particles get. The particles are captured as they tumble from theagglomerator. The particles are then dried to a desired moisture levelby any suitable mechanism, such as a rotary or fluid bed. In thisexample, a forced air rotary dryer 210 is used to lower the highmoisture content of the particles to less than about 15% by weight andideally about 8-13% by weight. At the outlet of the rotary dryer, theparticles are screened with sieves 212 or other suitable mechanism toseparate out the particles of the desired size range. Tests have shownthat about 80% or more of the particles produced by pan agglomerationwill be in the desired particle size range. Preferably, the yield ofparticles in the desired size range is 85% or above, and ideally 90% orhigher. The selected particle size range can be in the range of about 10mm to about 100 microns, and preferably about 2.5 mm or less. Anillustrative desired particle size range is 12×40 mesh (1650-400microns).

The exhaust from the dryer is sent to a baghouse for dust collection.Additional actives such as borax and fragrance can be added to theparticles at any point in the process before, during and/or afteragglomeration. Also, additional/different actives can be dry blendedwith the particles.

Illustrative composite absorbent particles after drying have a specificweight of from about 0.15 to about 1.2 kilograms per liter and a liquidabsorbing capability of from about 0.6 to about 2.5 liters of water perkilogram of particles. Preferably, the particles absorb about 50% ormore of their weight in moisture, more preferably about 75% or more oftheir weight in moisture, even more preferably greater thanapproximately 80% and ideally about 90% or more of their weight inmoisture.

Specific examples of compositions that can be fed to the agglomeratorusing the process of FIG. 2 include (in addition to effective amounts ofactive):

-   -   100% Bentonite Powder    -   67% Calcium Bentonite Clay (core) & 33% Bentonite Powder    -   50% Calcium Bentonite Clay (core) & 50% Bentonite Powder    -   Perlite (core) & Bentonite Powder    -   Sand (core) & Bentonite Powder

The following table lists illustrative properties for variouscompositions of particles created by a 20″ pan agglomerator at panangles of 40-60 degrees and pan speeds of 20-50 RPM. The total solidsflow rates into the pan were 0.2-1.0 kg/min.

TABLE 2 Bentonite Final Bulk Clump Core Water to Core Ratio MoistureDensity (kg/l) Strength None   15-23% 100:0    1.0-1.4% 0.70-0.78 95-97Calcium bentonite 15-23 50:50 3.4 0.60-0.66 95-97 Calcium bentonite15-18 33:67 4.3-4.4 0.57-0.60 93-95 Sand 10-12 50:50 2.0 0.81-0.85 97-98Sand 6-8 33:67 1.6-2.4 0.92 97 Perlite   15-19% 84:16 0.36-0.39 97%Perlite   16-23% 76:24 0.27-0.28   95-97%

Clump strength is measured by first generating a clump by pouring 10 mlof pooled cat urine (from several cats so it is not cat specific) onto a2 inch thick layer of litter. The urine causes the litter to clump. Theclump is then placed on a ½″ screen after a predetermined amount of time(e.g., 6 hours) has passed since the particles were wetted. The screenis agitated for 5 seconds with the arm up using a Ro-Tap MechanicalSieve Shaker made by W.S. Tyler, Inc. The percentage of particlesretained in the clump is calculated by dividing the weight of the clumpafter agitation by the weight of the clump before agitation. Referringagain to the table above, note that the clump strength indicates thepercentage of particles retained in the clump after 6 hours. Asshown, >90%, and more ideally, >95% of the particles are retained in aclump after 6 hours upon addition of an aqueous solution, such asdeionized water or animal urine. Note that ≧about 80% particle retentionin the clump is preferred. Also, note the reduction in bulk density whena core of calcium bentonite clay or perlite is used.

FIG. 4 is a process diagram illustrating another exemplary panagglomeration process 400 with a recycle subsystem 402. Save for therecycle subsystem, the system of FIG. 4 functions substantially the sameas described above with respect to FIG. 2. As shown in FIG. 4, particlesunder the desired size are sent back to the agglomerator. Particles overthe desired size are crushed in a crusher 404 and returned to theagglomerator.

The diverse types of clays and mediums that can be utilized to createabsorbent particles should not be limited to those cited above. Further,unit operations used to develop these particles include but should notbe limited to: high shear agglomeration processes, low shearagglomeration processes, high pressure agglomeration processes, lowpressure agglomeration processes, mix mullers, roll press compacters,pin mixers, batch tumble blending mixers (with or without liquidaddition), and rotary drum agglomerators. For simplicity, however, thelarger portion of this description shall refer to the pan agglomerationprocess, it being understood that other processes could potentially beutilized with similar results.

FIG. 5 is a process diagram illustrating an exemplary pin mixer process500 for forming composite absorbent particles. As shown, absorbentparticles and active are fed to a pin mixer 502. Water is also sprayedinto the mixer. The agglomerated particles are then dried in a dryer 504and sorted by size in a sieve screen system 506. The following tablelists illustrative properties for various compositions of particlescreated by pin mixing.

TABLE 3 Bentonite to Water Bulk Clump Strength - Lightweight Clay RatioAddition Density 6 hours Clay (wt %) (wt %) (lb/ft³) (% Retained)Zeolite (39 lb/ft³) 50:50 20 59 91 Bentonite 100:0  20 67 95 (64 lb/ft³)

FIG. 6 is a process diagram illustrating an exemplary mix muller process600 for forming composite absorbent particles. As shown, the variouscomponents and water and/or binder are added to a pellegrini mixer 602.The damp mixture is sent to a muller agglomerator 604 where the mixtureis agglomerated. The agglomerated particles are dried in a dryer 606,processed in a flake breaker 608, and then sorted by size in a sievescreen system 610.

The following table lists illustrative properties for variouscompositions of particles created by a muller process. Note that themoisture content of samples after drying is 2-6 weight percent.

TABLE 4 Ben- Water Calculated Actual Clump tonite: Addi- Bulk BulkStrength - Clay tion Density Density 6 hours Dust Clay (wt %) (wt %)(lb/ft³) (lb/ft³) (% Retained) (mg) GWC 50:50 33 43 45 83 39 (32 lb/ft³)GWC 50:50 47 43 42 56 34 (32 lb/ft³) Taft DE 50:50 29 33 46 86 38 (22lb/ft³) Taft DE 50:50 41 33 43 76 35 (22 lb/ft³)

The composite absorbent particle can be formed into any desired shape.For example, the particles are substantially spherical in shape whenthey leave the agglomeration pan. At this point, i.e., prior to drying,the particles have a high enough moisture content that they aremalleable. By molding, compaction, or other processes known in the art,the composite absorbent particle can be made into non-spherical shapessuch as, for example, ovals, flattened spheres, hexagons, triangles,squares, etc. and combinations thereof.

EXAMPLE 1

Referring again to FIG. 1, a method for making particles 102 isgenerally performed using a pan agglomeration process in which clayparticles of ≦200 mesh (≦74 microns), preferably ≦325 mesh (≦43 microns)particle size premixed with particles of active, are agglomerated in thepresence of an aqueous solution to form particles in the size range ofabout 12×40 mesh (about 1650-250 microns). Alternatively, the particlesare first formed with clay alone, then reintroduced into the pan ortumbler, and the active is added to the pan or tumbler, and a batch runis performed in the presence of water or a binder to adhere the activeto the surface of the particles. Alternatively, the active can besprayed onto the particles.

EXAMPLE 2

A method for making particles 104 is generally performed using theprocess described with relation to FIG. 2, except no core material isadded.

EXAMPLE 3

A method for making particles 106 is generally performed using theprocess described with relation to FIG. 2, except that introduction ofthe absorbent granules and the active into the agglomerator arealternated to form layers of each.

EXAMPLE 4

A method for making particles 108 is generally performed using theprocess described with relation to FIG. 2, except that the active hasbeen pre-clumped using a binder, and the clumps of active are added.Alternatively, particles of absorbent material can be created byagglomeration and spotted with a binder such that upon tumbling with anactive, the active sticks to the spots of binder thereby formingconcentrated areas. Yet another alternative includes the process ofpressing clumps of active into the absorptive material.

EXAMPLE 5

A method for making particles 110 is generally performed using theprocess described with relation to FIG. 2.

EXAMPLE 6

A method for making particles 112 is generally performed using theprocess described with relation to FIG. 2.

EXAMPLE 7 & 8

A method for making particles 114 and 116 are generally performed usingthe process described with relation to FIG. 2, except no active isadded.

In addition, the performance-enhancing active can be physicallydispersed along pores of the particle by suspending an insoluble activein a slurry and spraying the slurry onto the particles. The suspensiontravels into the pores and discontinuities, depositing the activetherein.

Control Over Particle Properties

Strategically controlling process and formulation variables along withagglomerate particle size distribution allows for the development ofvarious composite particles engineered specifically to enable attributeimprovements as needed. Pan agglomeration process variables include butare not limited to raw material and ingredient delivery methods, solidto process water mass ratio, pan speed, pan angle, scraper type andconfiguration, pan dimensions, throughput, and equipment selection.Formulation variables include but are not limited to raw materialspecifications, raw material or ingredient selection (actives, binders,clays and other solids media, and liquids), formulation of liquidsolution used by the agglomeration process, and levels of theseingredients.

The pan agglomeration process intrinsically produces agglomerates with anarrow particle size distribution (PSD). The PSD of the agglomerates canbe broadened by utilizing a pan agglomerator that continuously changesangle (pivots back and forth) during the agglomeration process. Forinstance, during the process, the pan could continuously switch from oneangle, to a shallower angle, and back to the initial angle or from oneangle, to a steeper angle, and back to the initial angle. This variableangle process would then repeat in a continuous fashion. The angles andrate at which the pan continuously varies can be specified to meet theoperator's desired PSD and other desired attributes of the agglomerates.

As mentioned above, the agglomeration process can be manipulated tocontrol process and formulation variables. This manipulation can beused, for example, to increase or decrease pore size, pore volume andsurface area which can then result in control of bulk properties such asthe bulk density of the particles (with or without use of corematerial),the overall liquid absorption capacity by the particles, andthe rate of degradation of formed granules under swelling conditions.The pore size, pore volume, surface area and resulting bulk propertiesdepend primarily on the pan angle and the pan speed, which togethercreate an effective pressure on the particles being agglomerated intocomposite particles. By increasing the pan speed, the centrifugal forceexerted on the particles is increased, thereby reducing the internalpore size of the resulting composite particles. Similarly, as the panangle is increased from the horizontal, the particles will tumble moreviolently towards the bottom of the pan, again reducing the internalpore size of the resulting composite particles.

A larger pore size results in a lower overall bulk density of thecomposite particles. A larger pore size also allows odoriferousmolecules to more readily reach actives embedded within the compositeparticles. The pore size also affects hydraulic conductivity.

By knowledge of interactions between pan, dryer, and formulationparameters one could further optimize process control orformulation/processing cost. For example, it was noted that by additionof a minor content of a less absorptive clay, we enabled easier processcontrol of particle size. For example, by addition of calcium bentoniteclay the process became much less sensitive to process upsets andmaintains consistent yields in particle size throughout normal moisturevariation. Addition of calcium bentonite clay also helped reduceparticle size even when higher moisture levels were used to improvegranule strength. This is of clear benefit as one looks at enhancingyields and having greater control over particle size minimizing need forcostly control equipment or monitoring tools.

For those practicing the invention, pan agglomeration manipulation andscale-up can be achieved through an empirical relationship describingthe particle's path in the pan. Process factors that impact the path theparticle travels in the pan include but are not limited to pandimensions, pan speed, pan angle, input feed rate, solids to processliquid mass ratio, spray pattern of process liquid spray, position ofscrapers, properties of solids being processed, and equipment selection.Additional factors that may be considered when using pan agglomeratorsinclude particle to particle interactions in the pan, gravity effects,and the following properties of the particles in the pan: distancetraveled, shape of the path traveled, momentum, rotational spin aboutaxis, shape, surface properties, and heat and mass transfer properties.

The composite particles provide meaningful benefits, particularly whenused as a cat litter, that include but are not limited to improvementsin final product attributes such as odor control, litter box maintenancebenefits, reduced dusting or sifting, and consumer convenience. As such,the following paragraphs shall discuss the composite absorbent particlesin the context of animal litter, it being understood that the conceptsdescribed therein apply to all embodiments of the absorbent particles.

Significant odor control improvements over current commercial litterformulas have been identified for, but are not limited to, the followingareas:

-   -   Fecal odor control (malodor source: feline feces)    -   Ammonia odor control (malodor source: feline urine)    -   Non-ammonia odor control (malodor source: feline urine)

Odor control actives that can be utilized to achieve these benefitsinclude but are not limited to powdered activated carbon, silica powder(Type C), borax pentahydrate, and bentonite powder. The odor controlactives are preferably distributed within and throughout theagglomerates by preblending the actives in a batch mixer with clay basesand other media prior to the agglomeration step. The pan agglomerationprocess, in conjunction with other unit operations described here,allows for the targeted delivery of actives within and throughout theagglomerate, in the outer volume of the agglomerate with a rigid core,on the exterior of the agglomerate, etc. These or any targeted activedelivery options could also be performed in the pan agglomerationprocess exclusively through novel approaches that include, but shouldnot be limited to, strategic feed and water spray locations, timedelayed feeders and spray systems, raw material selection and theircorresponding levels in the product's formula (actives, binders, clays,and other medium), and critical pan agglomeration process variablesdescribed herein.

Additionally, the pan agglomeration process allows for the incorporationof actives inside each agglomerate or granule by methods including butnot limited to dissolving, dispersing, or suspending the active in theliquid solution used in the agglomeration process. As the panagglomeration process builds the granules from the inside out, theactives in the process's liquid solution become encapsulated inside eachand every granule. This approach delivers benefits that include butshould not be limited to reduced or eliminated segregation of activesfrom base during shipping or handling (versus current processes thatsimply dry tumble blend solid actives with solid clays and medium),reduced variability in product performance due to less segregation ofactives, more uniform active dispersion across final product, improvedactive performance, and more efficient use of actives. This moreeffective use of actives reduces the concentration of active requiredfor the active to be effective, which in turn allows addition of costlyingredients that would have been impractical under prior methods. Forexample, dye or pigment can be added to vary the color of the litter,lighten the color of the litter, etc. Disinfectant can also be added tokill germs. For example, this novel approach can be utilized bydissolving borax pentahydrate in water. This allows the urease inhibitor(boron) to be located within each granule to provide ammonia odorcontrol and other benefits described here. One can strategically selectthe proper actives and their concentrations in the liquid solution usedin the process to control the final amount of active available in eachgranule of the product or in the product on a bulk basis to deliver thebenefits desired.

Targeted active delivery methods should not be limited to the targetedactive delivery options described here or to odor control activesexclusively. For example, another class of active that could utilizethis technology is animal health indicating actives such as a pHindicator that changes color when urinated upon, thereby indicating ahealth issue with the animal. This technology should not be limited tocat litter applications. Other potential industrial applications of thistechnology include but should not be limited to laundry, home care,water filtration, fertilizer, iron ore pelletizing, pharmaceutical,agriculture, waste and landfill remediation, and insecticideapplications. Such applications can utilize the aforementioned unitoperations like pan agglomeration and the novel process technologiesdescribed here to deliver smart time-releasing actives or other types ofactives and ingredients in a strategic manner. The targeted activedelivery approach delivers benefits that include but should not belimited to the cost efficient use of actives, improvements in activeperformance, timely activation of actives where needed, and improvementsin the consumer perceivable color of the active in the final product.One can strategically choose combinations of ingredients and targetedactive delivery methods to maximize the performance of actives in finalproducts such as those described here.

Litter box maintenance improvements can be attributed to proper controlof the product's physical characteristics such as bulk density, clumpstrength, attrition or durability (granule strength), clump height(reduction in clump height has been found to correlate to reducedsticking of litter to the bottom of litter box), airborne and visualdust, lightweight, absorption (higher absorption correlates to lesssticking to litter box—bottom, sides, and corners), adsorption, ease ofscooping, ease of carrying and handling product, and similar attributes.Strategically controlling process and formulation variables along withagglomerate particle size distribution allows for the development ofvarious cat litter particles engineered specifically to “dial in”attribute improvements as needed. Pan agglomeration process variablesinclude but are not limited to raw material and ingredient deliverymethods, solid to process water mass ratio, pan speed, pan angle,scraper type and configuration, pan dimensions, throughput, andequipment selection. Formulation variables include but are not limitedto raw material specifications, raw material or ingredient selection(actives, binders, clays and other solids medium, and liquids),formulation of liquid solution used by the agglomeration process, andlevels of these ingredients. For example, calcium bentonite can be addedto reduce sticking to the box.

Improvements in consumer convenience attributes include but are notlimited to those described here and have been linked to physicalcharacteristics of the product such as bulk density or light weight.Because the absorbent particles are made from small granules, the panagglomeration process creates agglomerated particles having a porousstructure that causes the bulk density of the agglomerates to be lowerthan its initial particulate form. Further, by adjusting the rotationspeed of the pan, porosity can be adjusted. In particular, a faster panrotation speed reduces the porosity by compressing the particles. Sinceconsumers use products like cat litter on a volume basis, the panagglomeration process allows the manufacturer to deliver bentonite basedcat litters at lower package weights but with equivalent volumes tocurrent commercial litters that use heavier clays that are simply mined,dried, and sized. The agglomerates' reduced bulk density alsocontributes to business improvements previously described such as costsavings, improved logistics, raw material conservation, and otherefficiencies. Lightweight benefits can also be enhanced by incorporatingcores that are lightweight. A preferred bulk density of a lightweightlitter according to the present invention is less than about 1.5 gramsper cubic centimeter and more preferably less than about 0.85 g/cc. Evenmore preferably, the bulk density of a lightweight litter according tothe present invention is between about 0.25 and 0.85 g/cc, and ideallyfor an animal litter 0.35 and 0.50 g/cc.

The porous structure of the particles also provides other benefits. Thevoids and pores in the particle allow access to active positionedtowards the center of the particle. This increased availability ofactive significantly reduces the amount of active required to beeffective. For example, in particles in which carbon is incorporated inlayers or heterogeneously throughout the particle, the porous structureof the absorbent particles makes the carbon in the center of theparticle available to control odors. Many odors are typically in the gasphase, so odorous molecules will travel into the pores, where they areadsorbed onto the carbon. By mixing carbon throughout the particles, theodor-absorbing life of the particles is also increased. This is due tothe fact that the agglomeration process allows the manufacturer tocontrol the porosity of particle, making active towards the center ofthe particle available.

Because of the unique processing of the absorbent particles of thepresent invention, substantially every absorbent particle containscarbon. As discussed above, other methods merely mix GAC with clay, andcompress the mixture into particles, resulting in aggregation and someparticles without any carbon. Thus, more carbon must be added. Again,because of the way the particles are formed and the materials used(small clay granules and PAC), lower levels of carbon are required toeffectively control odors. In general, the carbon is present in theamount of 5% or less based on the weight of the particle. Inillustrative embodiments, the carbon is present in the amount of 1.0% orless, 0.5% or less, and 0.3% or less, based on the weight of theparticle. In other embodiments, activated alumina is present in theamount of 1.0% or less, 0.5% or less, and 0.3% or less, based on theweight of the particle. This lower amount of carbon or other odorcontrolling additive significantly lowers the cost for the particles, asthese additives are very expensive compared to clay. The amount ofcarbon or other odor controlling additive required to be effective isfurther reduced because the agglomeration process incorporates thecarbon into each particle, using it more effectively. As shown in thegraph 700 of FIG. 7, the composite absorbent particles according to apreferred embodiment have a malodor rating below about 15, whereas thenon-agglomerated control has a rating of about 40, as determined by aMalodor Sensory Method.

Description of Malodor Sensory Method:

-   -   1. Cat boxes are filled with 2,500 cc of test litter.    -   2. Boxes are dosed each morning for four days with 30 g of        pooled feces.    -   3. On the fourth day the center of each box is dosed with 20 ml        pooled urine.    -   4. The boxes are placed into sensory evaluation booths.    -   5. The boxes are allowed to equilibrate in the closed booths for        30-45 minutes before panelist evaluation.    -   6. The samples are then rated on a 60 point line scale by        trained panelists.

Preferably, the agglomerated particles exhibit noticeably less odorafter four days from contamination with animal waste as compared to agenerally solid particle of the absorbent material alone undersubstantially similar conditions.

As mentioned above, the human objection to odor is not the only reasonthat it is desirable to reduce odors. Studies have shown that catsprefer litter with little or no smell. One theory is that cats like tomark their territory by urinating. When cats return to the litterbox anddon't sense their odor, they will try to mark their territory again. Thenet effect is that cats return to use the litter box more often if theodor of their markings is reduced.

Accordingly, the composite particles induce a cat to use the litter, andthus provide a mechanism to defeat a cat's instinct to mark itsterritory in areas other than the litter box.

A preferred embodiment of the present invention has a feline inducementto use index of at least 8, and ideally at least 9, as measured by thefollowing test.

Description of Feline Inducement to Use Index Test:

-   -   1. Cat boxes are filled with 2,500 cc of test litter of >95%        bentonite, ˜1% activated carbon, and may include other optional        actives. The cat boxes are each placed in an individual cage        having a floor area of 12 square feet.    -   2. One cat is placed in each cage and kept there for seven days.        The excrement and urine are not removed from the litter.    -   3. On the seventh day the cage is examined for urine and        excrement in areas other than the box.    -   4. The number of soiled areas of the cage other than the box are        enumerated and subtracted from a base number of 10 to produce        individual indices.        -   The individual indices are averaged by the total number of            cat boxes in the test to determine the feline inducement to            use index.

Additionally, in households with multiple cats, one or both cats mayobject to sharing the litterbox upon sensing the odor of the other cat'swaste. However, the superior odor control properties of the compositeparticles described herein have been found to sufficiently control odorsthat multiple cats use litter even after an extended period of time.

A preferred embodiment of the present invention has a multiple cat usageindex of at least 8, and ideally at least 9, as measured by thefollowing test.

Description of Multiple Cat Usage Index Test:

-   -   -   1. Cat boxes are filled with 2,500 cc of test litter of >95%            bentonite, ˜1% activated carbon, ˜1% of a boron compound            sprayed onto the particles, and optionally additional            actives. The cat boxes are each placed in an individual cage            having a floor area of 12 square feet.        -   2. Two cats are placed in each cage and kept there for seven            days. The excrement and urine are not removed from the            litter.        -   3. On the seventh day the cage is examined for urine and            excrement in areas other than the box.        -   4. The number of soiled areas of the cage other than the box            are enumerated and subtracted from a base number of 10 to            produce individual indices. The individual indices are            averaged by the total number of cat boxes in the test to            determine the multiple cat usage index.

The composite absorbent particles of the present invention exhibitsurprising additional features heretofore unknown. The agglomeratedcomposite particles allow specific engineering of the particle sizedistribution and density, and thereby the clump aspect ratio. Thus,hydraulic conductivity (K) values of ≦0.25 cm/s as measured by thefollowing method can be predicted using the technology disclosed herein,resulting in a litter that prevents seepage of urine to the bottom ofthe box when sufficient litter is present in the box.

Method for measuring Hydraulic Conductivity

Materials:

-   -   1. Water-tight gas drying tube with 7.5 centimeter diameter    -   2. Manometer    -   3. Stop watch    -   4. 250 ml graduated cylinder

Procedure:

-   -   1. Mix and weigh sample    -   2. Pour the sample into the Drying tube until the total height        of the sample is 14.6 centimeters.    -   3. Close the cell.    -   4. Use vacuum to pull air through and dry the sample for at        least 3 minutes.    -   5. When the sample is dry, saturate the sample slowly with water        by opening the inlet valve.    -   6. Allow the water exiting the drying tube to fill the graduated        cylinder.    -   7. Deair the system using vacuum, allowing the system to        stabilize for 10 minutes.    -   8. After 10 minutes, record the differential pressure as        displayed by the manometer.    -   9. Record at least 4 differential pressure measurements, waiting        3 minutes between each measurement.    -   10. Record the flow rate of the water entering the graduated        cylinder.    -   11. Calculate the Hydraulic Conductivity, K, using Darcy's Law        Q=−KA (ha-hb)/L        -   Q=Flow Rate        -   K=Hydraulic Conductivity        -   A=Cross Sectional Area        -   L=Bed Length        -   Ha-Hb=Differential Pressure

One of the distinguishing characteristics of the optimum K value is alitter clump with a very low height to length ratio (flat). Bycontrolling the particle size of the litter, clump strength and clumpprofile can be controlled. This is important because the smaller theclumps are, the less likely they are to stick to something like theanimal or litterbox. For instance, with prior art compacted litter, if acat urinates 1 inch from the side of the box, the urine will penetrateto the side of box and the clay will stick to the box. However, thepresent invention allows the litter particles to be engineered so urineonly penetrates about ½ inch into a mass of the particles.

Agglomerated composite particles according to the present invention alsoexhibit interesting clumping action not previously seen in theliterature. Particularly, the particles exhibit extraordinary clumpstrength with less sticking to the box, especially in compositeparticles containing bentonite and PAC. PAC is believed to act as arelease agent to reduce sticking to the box. However, intuitively thisshould also lead to reduced clump strength, not increased clumpstrength. The combination of stronger clumps yet exhibiting lesssticking to the box is both surprising and counter-intuitive. The resultis a litter with multiple consumer benefits including strong clumps, lowurine seepage, and little sticking to the box.

While not wishing to be bound by any particular theory, the increasedclump strength is believed to be due to at least some of thePAC-containing granules “falling apart” and releasing their bentoniteparticles to reorder themselves, and this ‘reordering’ produces astronger clump. As shown in FIGS. 8 and 9, this can best be described asa disintegration of more-water-soluble pieces of the agglomeratedcomposite particles 800 when in contact with moisture 802, allowing thepieces 804 of the particles to attach to surrounding particles. This“reordering” produces a stronger clump. In testing, the visualappearance of the cores is a signal that at least some of the granulesdecompose to smaller particles, and these particles are “suspending” inthe urine and are free to occupy interstitial spaces between particles,forming a stronger clump. This creates a network of softenedagglomerated particles where broken particle pieces are attaching toothers and creating a web of clumped material. Note however that theparticles described herein should not be limited to clumping orscoopable particles.

As mentioned above, the composite absorbent particles have particularapplication for use as an animal litter. The litter would then be addedto a receptacle (e.g., litterbox) with a closed bottom, a plurality ofinterconnected generally upright side walls forming an open top anddefining an inside surface. However, the particles should not be limitedto pet litters, but rather could be applied to a number of otherapplications such as:

-   -   Litter Additives—Formulated product can be pre-blended with        standard clumping or non-clumping clays to create a less        expensive product with some of the benefits described herein. A        post-additive product could also be sprinkled over or as an        amendment to the litter box.    -   Filters—Air or water filters could be improved by either        optimizing the position of actives into areas of likely contact,        such as the outer perimeter of a filter particle. Composite        particles with each subcomponent adding a benefit could also be        used to create multi-functional composites that work to        eliminate a wider range of contaminants.    -   Bioremediation/Hazardous/Spill Cleanup—Absorbents with actives        specifically chosen to attack a particular waste material could        be engineered using the technology described herein. Exemplary        waste materials include toxic waste, organic waste, hazardous        waste, and non-toxic waste.    -   Pharma/Ag—Medications, skin patches, fertilizers, herbicides,        insecticides, all typically use carriers blended with actives.        Utilization of the technology described herein reduce the amount        of active used (and the cost) while increasing efficacy.    -   Soaps, Detergents, and other Dry Products—Most dry household        products could be engineered to be lighter, stronger, longer        lasting, or cheaper using the technology as discussed above.    -   Mixtures of Different Particles—The composite particles can be        dry mixed with other types of particles, including but not        limited to other types of composite particles, extruded        particles, particles formed by crushing a source material, etc.        Mixing composite particles with other types of particles        provides the benefits provided by the composite particles while        allowing use of lower cost materials, such as crushed or        extruded bentonite. Illustrative ratios of composite particles        to other particles can be 75/25, 50/50, 25/75, or any other        ratio desired. For example, in an animal litter created by        mixing composite particles with extruded bentonite, a ratio of        50/50 will provide enhanced odor control, clumping and reduced        sticking, while reducing the weight of the litter and lowering        the overall cost of manufacturing the litter.    -   Mixtures of Composite Particles with Actives—The composite        particles can be dry mixed with actives, including but not        limited to particles of activated carbon.

ADDITIONAL EXAMPLES

Note that all percentages are in weight percent in the followingexamples.

EXAMPLE 9

A composite particle includes:

-   -   about 90-99.5% sodium bentonite as the primary absorbent        material about 0.1-10% activated carbon added to the sodium        bentonite as in particles 102-108 and 114 of FIG. 1    -   about 0-9.9% additional active

EXAMPLE 10

A composite particle includes:

-   -   about 90-99.5% sodium bentonite as the primary absorbent        material about 0.1-10% zeolite, crystalline silica, silica gel,        activated alumina, activated carbon, a superabsorbent polymer,        and mixtures thereof added to the sodium bentonite as in        particles 102-108 and 114 of FIG. 1    -   about 0-9.9% additional active

EXAMPLE 11

A composite particle includes:

-   -   about 10-70% core material selected from zeolite, crystalline        silica, silica gel, activated alumina, activated carbon, a        superabsorbent polymer, and mixtures thereof    -   about 30-90% sodium bentonite surrounding the core    -   about 0.1-10% activated carbon added to the sodium bentonite as        in particles 110-112 and 116 of FIG. 1    -   about 0-10% additional active

EXAMPLE 12

A composite particle includes:

-   -   about 10-70% core material selected from zeolite, crystalline        silica, silica gel, activated alumina, activated carbon, a        superabsorbent polymer, and mixtures thereof    -   about 30-90% sodium bentonite surrounding the core    -   about 0.1-25% zeolite, crystalline silica, silica gel, activated        alumina, a superabsorbent polymer, and mixtures thereof added to        the sodium bentonite as in particles 110-112 and 116 of FIG. 1    -   about 0-10% additional active

EXAMPLE 13

A composite particle includes:

-   -   about 10-70% core formed from agglomerated particles    -   about 30-90% sodium bentonite surrounding the core    -   about 0.1-25% zeolite, crystalline silica, silica gel, activated        alumina, a superabsorbent polymer, and mixtures thereof added to        the sodium bentonite as in particles 110-112 and 116 of FIG. 1    -   about 0-10% additional active

EXAMPLE 14

An absorbent composition of multiple composite particles, each compositeparticle including:

-   -   optional 10-70% core    -   about 30-100% agglomerated absorbent material    -   about 0.1-10% active added to the absorbent material as in        particles 102-116 of FIG. 1    -   about 0-10% additional active selected from an antimicrobial, an        odor reducing material, a binder, a fragrance, a health        indicating material, a color altering agent, a dust reducing        agent, a nonstick release agent, a superabsorbent material,        cyclodextrin, zeolite, activated carbon, a pH altering agent, a        salt forming material, a ricinoleate, silica gel, crystalline        silica, and mixtures thereof    -   where about 1-25% of the composite particles are colored for        creating “speckles” in the litter

EXAMPLE 15

An absorbent composition of multiple composite particles admixed withparticles of sodium bentonite, including:

-   -   about 10-90% particles of swellable sodium bentonite clay        particles, ˜1.4 mm-0.3 mm (14×50 mesh), dried and crushed    -   about 10-90% composite particles, each composite particle        including:        -   optional 10-70% core        -   about 30-100% agglomerated absorbent material        -   about 0.1-10% active added to the absorbent material as in            particles 102-116 of FIG. 1        -   about 0-10% additional active selected from an            antimicrobial, an odor reducing material, a binder, a            fragrance, a health indicating material, a color altering            agent, a dust reducing agent, a nonstick release agent, a            superabsorbent material, cyclodextrin, zeolite, activated            carbon, a pH altering agent, a salt forming material, a            ricinoleate, silica gel, crystalline silica, and mixtures            thereof    -   about 0-25% colored or white “speckles” in the litter (can be        activated alumina, colored composite particles, etc.)

The activated alumina itself may include an embedded coloring agent thathas been added during the fabrication of the activated aluminaparticles. The inventors have found that the odor absorbing propertiesof activated alumina are not significantly reduced due to theapplication of color altering agents thereto.

Additionally, activated alumina's natural white coloring makes it adesirable choice as a white, painted or dyed “speckle” in litters. Incomposite and other particles, the activated alumina can also be addedin an amount sufficient to lighten or otherwise alter the overall colorof the particle or the overall color of the entire composition.

Compositions may also contain visible but ineffective colored specklesfor visual appeal. Examples of speckle material are salt crystals orgypsum crystals.

EXAMPLE 16

An absorbent composition of multiple composite particles admixed withparticles of sodium bentonite, including:

-   -   about 10-90% composite particles, each composite particle        including:        -   optional 10-70% core        -   about 30-99.9% agglomerated absorbent material        -   about 0.1-10% active added to the absorbent material as in            particles 102-116 of FIG. 1        -   about 0-10% additional active selected from an            antimicrobial, an odor reducing material, a binder, a            fragrance, a health indicating material, a color altering            agent, a dust reducing agent, a nonstick release agent, a            superabsorbent material, cyclodextrin, zeolite, activated            carbon, a pH altering agent, a salt forming material, a            ricinoleate, silica gel, crystalline silica, and mixtures            thereof        -   about 0.01-50% particles of activated alumina dry mixed with            the composite particles. Preferably, the activated alumina            is present in the composition in an amount of about 0.01% to            about 50% of the composition by weight based on the total            weight of the absorbent composition. More preferably, the            activated alumina is present in the composition in an amount            of about 0.1% to about 25% by weight.

EXAMPLE 17

An absorbent composition (clumpable or nonclumpable) with improved odorcontrol includes:

-   -   about 0.1-25.0% activated alumina and/or zeolite and/or silica        particles about 0-75% additives    -   to 100% composite particles as in particles 102-116 of FIG. 1

EXAMPLE 18

An absorbent composition with antimicrobial benefit includes:

-   -   about 0.5-5.0% activated alumina and/or zeolite and/or silica        particles [odor control]    -   about 0.001-1.0% borax pentahydrate [antimicrobial]    -   about 0.001-10% fragrance    -   about 0-25% additional additives    -   to 100% composite particles as in particles 102-116 of FIG. 1

EXAMPLE 19

A clumping absorbent composition with antimicrobial benefit includes:

-   -   about 2% colored activated alumina and/or zeolite and/or silica        particles, 1-2 mm (10×18 mesh)    -   about 0.5% borax pentahydrate [antimicrobial]    -   about 0.71% spray-dried fragrance—sprayed onto starch beads and        mixed in    -   about 96.79% composite particles as in particles 102-116 of FIG.        1, ˜1.4 mm-0.3 mm (14×50 mesh), dried and crushed

EXAMPLE 20

The following composition provides the benefit of improved odor controlthroughout the litter due to the varying densities of zeolite,activated, alumina, and silica gel.

An absorbent composition that is either clumpable or nonclumpableincludes:

-   -   about 0.001-25.0% zeolite particles    -   about 0.001-25.0% activated alumina particles    -   about 0.001-25.0% silica gel particles    -   about 0-50% additives to 100% composite particles including        sodium bentonite clay as in particles 102-116 of FIG. 1

The zeolite is the heaviest of the three odor-absorbing materials,alumina is in the middle, and silica gel is the lightest. Because of thetendency of the materials to segregate upon agitation such as a catdigging in the litterbox, the zeolite, being heavier, will tend to movetowards the bottom of the litter, while the lighter silica gel will tendto migrate towards the top of the litter. Thus, the litter will containodor controlling actives throughout. An additional benefit is that thesilica gel tends to repel liquid running across it, making it the idealmaterial for the upper layer of litter, as it will not immediatelybecome saturated by animal urine but will retain its odor absorbingproperties.

Also, by adding a lighter material such silica (25 lbs/ft³) or zeolite(about 50 lbs/ft³), the overall weight per volume unit of the mixture isreduced.

For clumping litter not relying on binders for clump strength, the totalcontent of zeolite, activated alumina, and silica gel particles ispreferably less than about 25% so that the clay provides satisfactoryclumping performance.

EXAMPLE 21

In a variation of Example 20:

An absorbent composition that is either clumpable or nonclumpableincludes:

-   -   about 0.001-25.0% activated alumina particles    -   about 0.001-25.0% zeolite particles    -   about 0-50% additives    -   to 100% composite particles as in particles 102-116 of FIG. 1

EXAMPLE 22

In a variation of Example 20:

An absorbent composition that is either clumpable or nonclumpableincludes:

-   -   about 0.001-25.0% zeolite particles    -   about 0.001-25.0% silica gel particles    -   about 0-50% additives    -   to 100% composite particles as in particles 102-116 of FIG. 1

EXAMPLE 23

In a variation of Example 20:

An absorbent composition that is either clumpable or nonclumpableincludes:

-   -   about 0.001-25.0% activated alumina particles    -   about 0.001-25.0% silica gel particles    -   about 0-50% additives    -   to 100% composite particles as in particles 102-116 of FIG. 1

EXAMPLE 24

A flushable and clumping absorbent composition with improved odorcontrol includes:

-   -   about 0.1-25.0% activated alumina and/or zeolite and/or silica        particles about 0-75% additives    -   less than about 1% of a water soluble binding agent to 100%        composite particles as in particles 102-116 of FIG. 1

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of a preferred embodiment shouldnot be limited by any of the above-described exemplary embodiments, butshould be defined only in accordance with the following claims and theirequivalents.

What is claimed is:
 1. A method of making animal litter comprising:providing particles of sodium bentonite having a mean particle diameterof 3000 μm or less; providing particles of powdered activated carbon(PAC) having a mean particle diameter of less than 500 μm; bindingtogether said sodium bentonite with said PAC to form composite particlescomprising sodium bentonite and PAC; mixing said composite particleswith other types of particles; wherein the PAC is present in the animallitter in an amount of 5% or less based on the weight of the animallitter.
 2. The method of making animal litter recited in claim 1,wherein said binding step comprises combining said sodium bentonite andsaid PAC in a tumble/growth agglomeration process.
 3. The method ofmaking animal litter recited in claim 1, wherein said sodium bentoniteand said PAC are homogeneously distributed throughout the compositeparticles.
 4. The method of making animal litter recited in claim 1,wherein the mean particle diameter of the sodium bentonite is 25-150 μm.5. The method of making animal litter recited in claim 1, wherein themean particle diameter of the PAC is 25-150 μm.
 6. The method of makinganimal litter recited in claim 1, wherein the mean particle diameter ofthe sodium bentonite is 25-150 μm and the mean particle diameter of thePAC is 25-150 μm.
 7. The method of making animal litter recited in claim1, wherein the mean particle diameter of the sodium bentonite is 25-150μm, the mean particle diameter of the PAC is 25-150 μm, and thecomposite particles have a mean particle diameter of less than 2.5 mm.8. The method of making animal litter recited in claim 1, wherein themean particle diameter of the sodium bentonite is 25-150 μm, the meanparticle diameter of the PAC is 25-150 μm, and the composite particleshave a mean particle diameter of 400-1650 μm.
 9. The method of makinganimal litter recited in claim 2, wherein the mean particle diameter ofthe sodium bentonite is 25-150 μm, the mean particle diameter of the PACis 25-150 μm, and the composite particles have a mean particle diameterof 400-1650 μm.
 10. The method of making animal litter recited in claim3, wherein the mean particle diameter of the sodium bentonite is 25-150μm, the mean particle diameter of the PAC is 25-150 μm, and thecomposite particles have a mean particle diameter of 400-1650 μm. 11.The method of making animal litter recited in claim 1, wherein the PACis present in an amount from 0.3% to 1% based on the weight of theanimal litter.
 12. The method of making animal litter recited in claim8, wherein the PAC is present in an amount from 0.3% to 1% based on theweight of the animal litter.
 13. The method of making animal litterrecited in claim 9, wherein the PAC is present in an amount from 0.3% to1% based on the weight of the animal litter.
 14. The method of makinganimal litter recited in claim 10, wherein the PAC is present in anamount from 0.3% to 1% based on the weight of the animal litter.
 15. Themethod of making animal litter recited in claim 1, wherein the PAC ispresent in an amount less than 1% based on the weight of the animallitter.
 16. The method of making animal litter recited in claim 8,wherein the PAC is present in an amount less than 1% based on the weightof the animal litter.
 17. The method of making animal litter recited inclaim 9, wherein the PAC is present in an amount less than 1% based onthe weight of the animal litter.
 18. The method of making cat litterrecited in claim 10, wherein the PAC is present in an amount less than1% based on the weight of the animal litter.